For glyphosate-based herbicides like Roundup, a non-ionic surfactant (NIS) should typically be added at a rate of 0.25% to 1.0% of the total spray solution volume.
Understanding Surfactant Use with Glyphosate (Roundup)
Adding a surfactant is crucial for maximizing the effectiveness of many glyphosate formulations, including Roundup. Surfactants, particularly non-ionic surfactants (NIS), help the herbicide spread evenly and penetrate the waxy surface of plant leaves, leading to better absorption and more consistent weed control.
Recommended Surfactant Rates
The exact amount of surfactant to use depends on the specific glyphosate product and the type of surfactant. Always consult your product's label for precise instructions, as some Roundup formulations may already contain a surfactant. However, for products requiring an external surfactant, the general recommendation for a non-ionic surfactant is:
- Percentage Rate: 0.25% to 1.0% of the total spray solution volume.
- Volume Rate (for large applications): This translates to 1 quart to 1 gallon of non-ionic surfactant per 100 gallons of spray solution.
Practical Application Rates for Common Sprayer Sizes
To help you measure the correct amount for smaller sprayers often used in home gardens or small acreage, here's a general guide based on the recommended percentage range. Remember that 1 fluid ounce (fl oz) is approximately 2 tablespoons (tbsp) or 6 teaspoons (tsp).
| Total Spray Volume | Minimum Surfactant (0.25%) | Maximum Surfactant (1.0%) |
|---|---|---|
| 1 Gallon | 0.32 fl oz (approx. 2 tsp) | 1.28 fl oz (approx. 1 tbsp + 1 tsp) |
| 2 Gallons | 0.64 fl oz (approx. 1 tbsp + 1 tsp) | 2.56 fl oz (approx. 2.5 tbsp) |
| 3 Gallons | 0.96 fl oz (approx. 2 tbsp) | 3.84 fl oz (approx. 3.5 tbsp) |
| 100 Gallons | 1 quart | 1 gallon |
Note: These are general guidelines. Always refer to the specific herbicide product label and the surfactant product label for the most accurate and safe application rates. Individual product formulations may vary.
Why Use a Surfactant with Glyphosate?
Glyphosate works by being absorbed through the leaves of weeds and translocated throughout the plant. Many weeds have a waxy cuticle on their leaves that can repel water-based sprays. A non-ionic surfactant helps to:
- Reduce Surface Tension: Allows the spray droplets to spread out more thinly and evenly over the leaf surface, rather than beading up.
- Improve Wetting: Ensures more of the leaf surface is covered by the herbicide solution.
- Enhance Penetration: Facilitates the movement of glyphosate through the waxy layer into the plant's vascular system.
Without an effective surfactant, a significant portion of the herbicide may simply run off the leaves or not be absorbed efficiently, reducing its effectiveness and potentially requiring repeat applications.
For more detailed information on maximizing herbicide effectiveness, consult resources from agricultural extension services, such as those provided by Oklahoma State University Extension.
